Ignition plug for internal-combustion engines



' 'June 22,- 1954 J. BLEUZE IGNITION PLUG FOR INTERNAL-COMBUSTION ENGINES Filed oct. 18, 1951 /NvENTo/Q TMQuEs lsv/suza Patented June 22, 1954 IGNITION PLUG FOR INTERNAL- COMBUSTION ENGINES Jacques Bleuze, Paris, Fra

pagnie Generale de Tele poration of France nce, assignor to Comgraphie lSans Eliiil, a :cor-

Application Got-ober 18, 1951, lSerial No. '251,937

Claims priority, application France October 26, 1950 6 Claims.

The present invention refers to sparking plugs `for electric sparks such as the ignition plugs for internal combustion engines. It more particularly covers the ignition systems in which the feeding is made from a steep wave front.

The engine ignition plugs used so far are well known. The ignition plugs include a metallic envelope bearing one or several electrodes, and a central conductor insulated from the envelope, l in which it is engaged so that one of its ends be disposed close to the said electrodes. A dielectric mass lls a part of the envelope, blocking it up hermetically. Its purpose is to ensure the plug air-tightness and to electrically insulate the 1 said central conductor which passes through it. When a high voltage is abruptly applied between the envelope and the central conductor, a spark flashes between the latter and the one or several generator giving a very 6 electrodes supported by the envelope, so allowing to ignite the air-carburetant mixture in the cylinder of an explosion engine.

The said dielectric mass therefore must stand against high electric voltages, It also must stand against abrupt thermic shocks and considerable mechanical strains, due to the high temperatures and strong pressures produced by the explosion of the air-carburetant mixture.

Furthermore, the mass of electric insulation,

owing to its very nature, has a very small thermic conductibility (of the order of one thousand times inferior to the thermic conductibility of the usual metals).

Therefore, this insulation, heats up during the working of the engine, and

reaches a very high. temperature of steady worling, which entails very serious inconveniences. Indeed, at high temperatures, the electric resistance of the insulation decreases exponentially, with respect to the temperature, and may fall to Very small values` ances of the engines using the ignition systems such as Delco or magnetd which produce voltage wave fronts of 105 to 1()6 volts/seconda? and can ensure a correct ignition but as long as the insulation resistance of the spark plug is superior to 106 to 105 ohms. rlhis fact limits the acceptable temperature of steady working of the ignition plug, and whereby, imposes wcrlringm limits to the engine. This inconvenience is attenuated by the utilisation of electronic circuit breaking or electrostatic ignition systems. These systems produce very steep wave fronts, in the range of 1010 to 1011 volts/second and iunction,l correctly with small insulation resstances of the order of 10,3 ohms.

This limits the perform- These systems allow to push the steady working of the engines more. However, at the high rates of steady working, a very serious incon. venience happens, due to the very construction -of the ignition plugs.

the ends of the metallic piece,

Indeed, a very high ltemperature is applied to the point of the central conductor by the fact ol the vbad thermic conductibi-lity of the insulator which bears it. The temperature of that point can wherefore become high enough as to provoke untimely ignitions (back flame), which are injurious for the good working -of the engine, and let it rapidly go out of use.

The obj-ect -of -the present invention is a new type of Yignition plug, in which the heating of the Ipoint fof the central conductor is .sutciently limited to avoid the auto-ignition accident, and allow a .correct working on engines having a high rate of steady working.

Another object of the invention is a new type stable making, in which namely the electric insulator is no lmore necessary to ensure the air tightness -of that ignition -plug` According to the invention, the new type 4of ignition plug, intended more yparticularly to worl; with an `electrostatic feeding, is characterized by the presence Vof an organ joining the point of the central 'conductor to the envelope of the ignition plug, lthis organ .being a good heat conductor and also offering a high impedance for the shock wave Jof the voltage impulses as supplied by the said `feeding. Preferably, this organ is constituted by a .metallic piece, the form oi which .is :such .as to `present a certain coeiicient of self-induction. This coeicient is so adjusted that the `shock wave .may give a voltage between sufficient to let a spark :flash between the electrodes of the igniu `tion plug.

4According Lto a -rst mode -of embodiment, the ignition plug includes .a vmetallic envelope and a central Iconductor electrically insulated from the latter. Furthermore, it includes a metallic piece having the form of asolenoid whose `snires are insulated from `each other by an insulating material placed between them, this vpiece being disposed -in the Ybody of the ignition plug, coaXia-lly with the central conductor. It is fixed at one-endof that `centralconductoron one hand and nto the ignition plug body on the other hand.

According to a second way of embodiment, the said `piece will be constituted vby a metallic solenoid 'including a magnetic core coaxial to the central conductor, this lcore being made of Aa fire proof 'and insulating magnetic material Isuch yas the ferritea cylinder ,is 'fixed to the central conducto-rnear its point, the external cylinder is supported by a holder formed by the body of the ignition plug, these two cylinders being joined together at their free end, by a metallic piece, so as to form an inner side ensuring the air-tightness of the ignition plug.

The enclosed figures, as non-limiting examples, will allow the better understanding of the invention.

The Figure 1 shows schematically a classical ignition plug in longitudinal section.

The 1figure 2 shows the theoretical diagram of the invention.

The Figures 3, 4 and 5, schematically, show three modes of embodiment of ignition plugs, in longitudinal section, according to the invention.

The classical ignition plug represented on Figure l includes a metallic envelope 3, a central conductor 2 insulated from the envelope by an insulator il. The lower end of the central conductor 2 and that of the body 3, constitute the electrodes I between which the spark flashes.

On the Figure 2, the ignition plug has been represented by a spark gap I. This spark gap is fed by a generator II) loading a capacitor C and the spark flashes in I when closing the switch D (which, in the engine, is a distributorl driven by an appropriated mechanism).

The inductance connected between the point A and the earth does not short-circuit the spark gap, the wave front being blocked by this inductance. But if it is conveniently embodied,

the latter may, by thermic conductibility, easily" evacuate the heat from the point A.

In order that 3 makes a good blocking of the wave iront, the inductance value should be as high as possible. The value of this inductance will be easily increased, without increasing its size, by using fire prooi and insulating magnetic cores, such as ferrites, agglomerated iron powders, etc. This permits to give the inductance a compact form allowing better to evacuate the heatl from the point of the central conductor.

The ignition plug represented on Figure 3 includes a metallic envelope I in which the central conductor is placed. The latter, as well as the envelope are ended by the electrodes 4 disposed A metallic piece 3, of`

in iront of each other. solenoidal form, whose spires are insulated from each other by an insulating material 6, is fixed one end at the extremity of the central conductor in 8 and the other end at the envelope in 5. rlhe central conductor clears out in a cylindrical hollow I2 lined up with an insulating coat 1 which, together with the piece II fixed to the central conductor and bearing against this coat, ensures the air-tightness of the ignition plug.

The ignition plug represented on Figure 4 in- 4 cludes the same elements as in Figure 3, but furthermore, it includes a magnetic core I3 disposed in the solenoid 3 so increasing its coeillcient of self induction, and allowing to give to the solenoid a more compact form, so as to decrease the length of thermic conduction between the point of the central conductor and the envelope of the ignition plug.

The ignition plug represented on the Figure 5 includes a metallic envelope I and a central conductor 2 ended by electrodes 4 disposed in front of each other, a iirst metallic cylinder 3 fixed in 8 at the end of the central conductor, a second cylinder I4, coaxial to the first one as well as to the central conductor. This second cylinder bears against the envelope upon a conical bearing 5 and is joined to the cylinder 3 by a metallic annular piece I3. A coat of iireproof insulating the cylinder 3 between which it is laid. It also isolates the terminal piece II fixed to the central conductor 2, from the envelope I. In this embodiment, the air-tightness of the ignition plug is ensured by the two coaxial cylinders 3 and 4 and the piece I3 which joins them, and these three pieces form a short length of shortcircuited coaxial, equivalent to an inductance increased by a coat of fire proof and insulating magnetic material 6, laid between the two cylinders. It may be noticed that the present invention allows to embody ignition plugs, the airtightness of which is ensured by metallic pieces, a fact which overturns the technics of ignition plug construction in which their airtightness was ensured by an insulating mass.

What claim is:

l. An ignition plug more particularly intended for internal combustion engines, including a metallic envelope, a central conductor electrically insulated from this envelope, and a helical piece oering a substantial self induction coefficient, this piece joining one end oi the said central conductor to the envelope oi the ignition plug.

2. An ignition plug according to claim 1 in which the said helical piece is made in the form of a solenoid.

3. An ignition plug according to claim l, in which the said piece has the form of a solenoid, the spires of which are insulated roin each other by an insulating material disposed between them.

4. ,An ignition plug according to claim l, in which the said piece includes a core of insulating magnetic material, so increasing the sell induction coefficient of that piece. v

5. A spark plug for use with an internal combustion engine employing a direct current voltage impulse system comprising in combination a metallic tubular envelope, a central conductor located in said envelope and insulated therefrom, one end of said central conductor forming with the corresponding edge of said envelope a spark gap, and a metallic piece presenting two ends and looped so as to present a substantial selieinductance, o-ne of the ends of said piece being fastened to the end of the central conductor near the spark gap and the second end of said piece being fastened to said envelope.

6. A spark plug for use with an. internal oombustion engine employing direct current voltage impulse system comprising combination a metallic tubular envelope, a central conductor located in said envelope and insulated therefrom, one end of said central conductor forming with the corresponding edge of said envelope a spark gap, and a metallic helix surrounding said central conductor, one ci the ends of said helix being fastened to the end of the central conductor near the spark gap and the second end of said helix being fastened to said envelope.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,125,035 Smits July 26, 1938 2,372,429 Jones Mar. 2'?, 1945 2,408,881 Rettenmeyer Get. 8, 1945 2,461,168 Mcllvaine Feb. 8, 1949 2,590,168 Felici Mar. 25, 1952 

